Conventional turbomachines (also referred to as turbines), such as steam turbines, generally include a casing enclosing a rotating shaft (also referred to as a rotor) and a plurality of radially extending rows of blades affixed to the shaft. Pressurized steam directed onto the blades causes blade and shaft rotation. The serial steam path typically includes a steam inlet, a plurality of steam pressure zones within the turbine and a steam outlet.
Conventionally, the steam turbomachine (turbine) is segregated into a plurality of pressure zones between successive stages of stationary and rotating blade rows. The turbine blade geometries and configurations are intended to maximize the efficiency of deriving energy from the steam flow, thus increasing the overall efficiency of an electrical generating plant which utilizes the steam turbomachine (e.g., to drive an electric generator).
Regions where the steam turbine shaft penetrates the turbine casing are sealed to prevent the escape of pressurized steam from the casing. Further, in order to improve turbine efficiency, conventional turbine designs have utilized inter-stage seals to prevent steam from bypassing stage stationary blades or by-passing rotating blades through the gap between stationary and rotating components.
Steam swirls, caused by rotating components or blades, once getting into cavities between seal teeth, can generate unsteady aerodynamic forces. Such forces acting on rotor surface can lead to rotor instability. As more and tighter seals are used to improve turbomachine efficiency, swirl-induced rotor-dynamic instability becomes more and more significant, especially for large steam turbines. To improve rotor-dynamic stability, anti-swirl teeth or swirl breaks have been used to kill swirl or reverse swirl direction. Conventional anti-swirl or swirl break devices have to be positioned at a tight clearance with rotor surface to render them effective. However, those devices are not rub-friendly. To avoid hard rubbing (e.g., contact between stationary and rotating components), the conventional anti-swirl devices are attached to a packing ring which is flexibly attached to stationary component with a spring element that biases the ring to close. Such an approach requires considerable space in turbomachine. Advances in turbomachine technology have also reduced the spacing between components in the turbomachines, making it more difficult to implement traditional anti-swirl rings in the fluid flow path. As such, current approaches for addressing fluid swirl in turbomachines are lacking in one or more respects.